Ever since the discovery of X-ray radiation, attempts have been made to design X-ray microscopes (See "X-Ray Microscope" by Kirkpatrick and Pattee, pp 305-336, Handbuck der Physik, Volume 30, 1957.) Except for contact microradiography and the projection microscope where pencil beams of X-ray are used to project an image with little or no magnification, all X-ray microscopes with significant magnifications include systems of electron beam optics. They are in reality electron microscopes equipped with X-ray detectors. The fact that the refractive index of all known optical materials for X-ray is almost exactly unity precludes any design consideration of optical lenses. At grazing incidences, X-ray photons have been known for sometime to behave like light photons, but this knowledge was not successfully applied in any optical system until the late 1960's.
The limiting resolution of a light microscope is of the order of one-half the light wavelength, and this implies a limit of magnification to two to three thousand times. In practice, most light microscopes cannot magnify more than one thousand times. With electron microscopes, a beam of electrons is focused by electromagnetic lenses, and the wavelength of the energetic electrons are subatomic, or under one A. The resolution of the electron microscopes is, however, not limited by the electron wavelength, but by the stability of the beam-lens interactions. With great effort to stabilize the power supplies of the lenses, the beam, and to limit the dispersion of the electron cloud where each electron in the beam carries a repulsive charge to all others and contributes to aberation, the point resolution can reach a few A. Line resolution can generally do better than the point resolution. More recently, scanning electron microscopes (SEM) have gained great popularity. The beam spot for a typical SEM that focuses on and scans over a specimen is usually larger than 100 A, and with synchronous motion between the scan command and the cathode ray sweep on a screen, only one electron detector is required for SEM (U.S. Pat. No. 3,191,028 by Albert V. Crewe, 1965.) Heavy elements, particularly heavy metals, have a dense electron cloud and are opaque to the electron beam. Staining with heavy metals for very thin specimen becomes a necessary step for transmission electron microscopy, while coating with heavy metals shows surface details for SEM. The use of heavy metals becomes particularly attractive when they are coated (evaporated) onto the specimen from an oblique angle. With shadows (no coating) and bright spots (heavy coating), the surface structure can be viewed in a beautiful three-dimentional perspective. A great number of techniques have been developed over the years to treat specimens with heavy metals. The fact that the heavy element under consideration is a known designated element with well defined characteristic adsorption edges is an important design consideration for a scanning X-ray microscope (SXM) or atom specific microscope ASM. A primary aim of the present invention is, with the help of certain atom specific optics, to obtain good resolution and image details. By modulating any set of X-ray bands of interest, all elements in the periodic table can be searched for, and SXM [or] ASM can also be engaged for elemental analysis, but this is not a primary aim.
When the electron detector of an electron microscope is replaced by a X-ray photon detector, the system can function as a "X-ray microanalyzer" instead of a transmission electron microscope, and can function as an X-ray microscope with scanning electron detection, X-ray detectors, on the other hand, often include a multichannel analyzer in order to distinguish one element from another and a low noise photo-detector, such as a liquid nitrogen cooled solid state detector. With a vacuum housing for the electron beam and the specimen, with electromagnetic lenses and their stable power supplier, plus various photoanalyzer equipments, the microscope becomes complex and expensive. The present invention uses only a simple system in which a beam of modulated X-rays with discriminating bands of interest for a certain designated element, focuses the beam onto a small spot, scans the beam over the specimen and displays an image without the use of a vacuum, low noise detector electronics, or a multichannel analyzer.